World's largest yachts

The "A" (ex Sigma) was constructed by Blohm and Voss at the HDW shipyard in Kiel, Germany, and features some of the most interesting architecture on the list. Perhaps the most prominent feature is the upside hull creating its angular, submarine-like shape. This feature makes it harder for intruders to board. "A" was launched in 2008 and was named after the owners, Andrey and Aleksandra Melnichenko.

It is thought to have cost somewhere around $300 million and boasts nearly 24,000 square feet of livable space. Interior features are far more stunning than its unusual exterior. It's filled with such luxuries as; $40,000 bath knobs, a room covered in white sting-ray hides, and an impressive master suite.

The vessel is outfitted with a state of the art security system. The master suite is bomb proof, and is accessible only at the top of a spiral staircase lined with scalloped, silver-leaf walls and a $60,000 banister.

Once at the top, the suite is protected by a biometric fingerprint security system. The ship has 44 security cameras on board with over a dozen exterior cameras outfitted with motion-detectors and a night-vision infrared system.

The crew of 37 includes a specialist for surfing, jet skiing, water skiing and cycling. The massive yacht can accommodate 14 guests in the owner's suite and six guest cabins. It costs over $20 million a year to maintain, and $500,000 to fuel. It is not available for charter.